DESIGN AND ANALYSIS OF SYNCHROMESH GEAR BOX
ABSTRACT
The main objective of this paper is to perform the mechanical design of the synchromesh gearbox and analysis of gears in the gearbox. We have taken grey cast iron and aluminium alloy materials for conducting the analysis. Presently used materials for gears and gear shafts are Cast Iron, Cast Steel. Therefore, in the paper, we are checking as aluminium can be the other material for the synchromesh gearbox for light utility vehicles so we can reduce the weight.
Keywords: Synchromesh gearbox, Structural Analysis, Design and Structural Analysis of the synchromesh gearbox.
INTRODUCTION
The most basic definition of a gearbox is that it is a contained gear train, or a mechanical unit or component consisting of a series of integrated gears within a housing. The name itself defines what it is — a box containing gears. In the most basic sense, a gearbox functions like any system of gears; it alters torque and speed between a driving device like a motor and a load.
The gears inside of a gearbox can be any one of several types from bevel gears and spiral bevel gears to worm gears and others such as planetary gears. The gears are mounted on shafts, which are supported by and rotated via rolling element bearings. The gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed.
Gearboxes are used in many applications including machine tools, industrial equipment, conveyors, and any rotary motion power transmission application that requires changes to torque and speed requirements.
So it’s clear — a gearbox is always a fully integrated mechanical component consisting of a series of mating gears contained in a housing with shafts and bearings (to support and resolve loads) and in many cases a flange for motor mounting. Most of the motion industry makes no differentiation between the terms gearhead and gearbox. But in a few contexts, the term gearbox specifically refers to housed gearing as described above while the more general term gearhead refers to assemblies otherwise open gearing that installs within some existing machine frame. The latter is targeted to compact or battery-powered mobile designs necessitating especially tight integration and omission of extra subcomponents. Here, a series of parallel plates might support the gear-train shafts (and their bearings) and allow bolting to a motor face.
As you know, there are three types of Gearbox. They are
- Sliding Mesh Gearbox
- Constant Mesh Gearbox
- Synchromesh Gearbox
In this paper, we will be focusing more on the synchromesh gearbox.
- Function
Synchromesh Gearbox is similar to the Constant Mesh Gearbox in which dog clutches in the Constant Mesh Gearbox are replaced by Synchromesh devices for smoother engagement of gears.
The gears on the main shaft are free to rotate w.r.t the main shaft whereas the gears on the lay shaft are fixed I.e. there is no relative motion between them.
- Construction
The figure shown below explains the construction and working of the Synchromesh Gearbox. Earlier, the synchromesh devices were fitted only to the higher gears. However, for the reverse gear and lower gears, ordinary dog clutches are provided and it is done to reduce the cost of the gearbox. The figure shown below consists of Gears B, C, D, and E attached to the main shaft A and are free to rotate and are always in mesh with the gears on the lay shaft. As long as the main shaft A rotates, the gears connected with the main shaft also rotate. The synchromesh device is placed in between the two Gears similar to dog clutches in a constant mesh gearbox.
The following terms are related to the synchromesh device and the gears surrounding it.
F1 & F2 → Free to slide on Splines
G1 & G2 → Ring Shaped members having internal teeth fits onto the external teeth of F1
& F2.
K1 & K2 → Dogteeth on B & D resp.
L1 & L2 → Dogteeth on C & E resp.
S1 & S2 → Forks (Gear changing levers)
T1 & T2 → Balls supported by springs.
M1, M2, N1, N2, P1, P2, R1, and R2 → Frictional surfaces.
- Working
The gears B, C, D and E are placed on the bearings connected to the main shaft. The Synchromesh Device, which has internal splines are placed in between the two gears. This is placed on the external splines of the main shaft. The internal gear G1 meshes with external gear F1.
First Gear:
When the main shaft A rotates, the power will be transferred to gear U3 of the lay shaft, which rotates Gear D of the main shaft.
Now for the engagement of gear D, the synchromesh device has to be slid towards the left with the help of Fork S2 so that the tapered surfaces P1 and P2 mesh with each other.
As the P2 is moving with some speed, the same speed will be given to the P1 because they are in contact with each other. Hence, the synchromesh device starts rotating.
The internal gear G2 is attached to the F2 also slides towards the left so that it can mesh onto the Gear K2.
Now, after meshing, the power is to be transferred from
B→ U1→ U3→ D→ F2→ Splines→ Main shaft.
The resultant figure will be
Second Gear:
When the Main shaft A rotates, the power will be transferred to the gear U2 of the lay shaft which rotates Gear C of the main shaft.
Now for the engagement of gear C, the synchromesh device has to be slid towards the right with the help of Fork S1 so that the tapered surface N1 and N2 mesh with each other.
As the N2 is moving with some speed, the same speed will be given to the N1 because they are in contact with each other. Hence, the synchromesh device starts rotating.
The internal gear G1 is attached to the F1 and also slides towards the right so that it can mesh onto the Gear L1.
Now, after meshing, the power is to be transferred from
B→ U1→ U2→ C→ F1→ Splines→ Main shaft.
The resultant figure will be
Third Gear:
When the Main shaft A rotates, the power will be transferred to gear B of the main shaft.
Now for the engagement of gear B, the synchromesh device has to be slid towards the
Left with the help of Fork S1 so that the tapered surface M1 and M2 mesh with each other.
As the M2 is moving with some speed, the same speed will be given to the M1 because they are in contact with each other. Hence, the synchromesh device starts rotating.
The internal gear G1 is attached to the F1 and also slides towards the left so it can mesh onto the Gear K1.
Now, after meshing, the power is to be transferred from
B→ F1→ Splines→ Main shaft.
The resultant figure will be
Reverse Gear:
When the main shaft A rotates, the power will be transferred to the gears U4 and U5 of the lay shaft rotates Gear E of the main shaft.
Now for the engagement of the gear E, the synchromesh device has to be slid towards the
Right with the help of Fork S2 the tapered surfaces R1 and R2 mesh with each other.
As the R2 is moving with some speed, the same speed will be given to the R1 because they are in contact with each other. Hence, the synchromesh device starts rotating.
The internal gear G2 which is attached to the F2 also slides towards the Right so that it can mesh onto the Gear L2.
Now, after meshing, the power is to be transferred from
B→ U1→ U4→ U5→ E→ F2→ Splines→ Main shaft.
- DESIGN AND CALCULATIONS OF A HELICAL GEAR PAIR
The design calculation of the helical gear pair has the following steps. The material for the gear pairs is taken as AISI 5160 OQT400. TABLE I shows the parameters considered for designing a helical gear.
Table 1: Parameters considered for the design of a helical gear
- MODELLING OF HELICAL GEAR
In this paper, AISI 5160 OQT 400 is used as the helical gear material. The material properties of AISI 5160 OQT 400 are given in the TABLE.
The procedure to model the gear of 34 number teeth with the combination of the all above-mentioned parameters in the Solid Works software, and another set of gears is modelled similarly. The figure shows a solid model of helical gear generated by Solid Works software.
The finite Element Method is a numerical technique for finding approximate solutions to boundary value problems. A boundary value problem is a differential equation with a set of additional restraints, called boundary conditions. FEM uses various methods to minimize an error function and produce a stable solution.
The need for Synchromesh Gearbox:
With the usage of Dog Clutches, the noise produced is low and the efficiency is high compared to the Sliding Mesh Gearbox.
The friction between the dog clutch and the associated gear will be less and due to this, there is a possibility of slip. To avoid this, the Synchronizers are used so they can engage smoothly with the gears and there will be no slippage.
VII. CONCLUSION
The helix angle is an important geometrical parameter in determining the state of stresses during the design of gears. The helix angle ψ is always measured on the cylindrical pitch surface. It ranges between 10˚ and 45˚. Commonly used values are 15, 23, 30 or 45˚. Lower values give less end thrust. Higher values result in smoother operation and more end thrust. In single helical gears, the helix angle ranges from 20° to 35°, while for double helical gears(herringbone gears), it may be made up to 45°. Keeping the face width, gear ratio, speed, and module constant and for variation of helix angle, the von-Mises stress decreases linearly. The helix angle of 23˚, corresponding to the range of helix angle is taken for further optimization.
IX. REFERENCES
1. Dadi vijay et.al, ‘Design And Structural Analysis Of High-Speed Helical Gear Using ANSYS’ Department of Mechanical Engineering Kakinada Institute of Technology And Science, Divili(2016).
2. Parth J. Bhatt et.al, ‘Material optimization of high speed single helical gear by using FEA approach ‘PG student, department of mechanical engineering Noble group of institute Junagadh — 362 001, India(2016)
3. K.C.Lathiya et.al, ‘Design modification and Failure Analysis of Damper Spring of 310 D.P.A of Single Plate Clutch System’Mechanical, Noble Group of Institution Junagadh (2015)
4. B.Venkatesh et.al, ‘Parametric investigation of the combined effect of Gear parameters on Tangential Force and Dynamic Tooth Load of 40 Ni2 Cr1 Mo 28 Steel Helical Gear’ Vardhaman College of Engineering, Hyderabad, India((2014)
5. B. Venkatesh et.al, ‘Effect of Bending Stress on Steel Alloy Of Helical Gear For High-Speed Applications’ Department of Mechanical Engineering, Vardhaman College of Engineering, India(2014).
6. J. Venkatesh, P. B. G. S. N. Murthy, “Design & Structural analysis of High-Speed Helical Gear by using Ansys,” IJERA., India, vol. 4, Issue 3, pp. 01–05, (2014 )
7. A. Sathyanarayana Achari et.al,‘A Comparison of Bending Stress and Contact Stress of a Helical Gear as Calculated by AGMA standard and FEA’ M.Tech Scholar, Department of Mechanical Engineering, NMAMIT, Nitte, Karnataka, India(2014)
